demand cap analysis
TRANSCRIPT
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THEUPPERBASINVOLUNTARYDEMANDCAPASAMEANSOFMITIGATINGLEGALUNCERTAINTYINTHECOLORADORIVERBASIN:MODELINGRESULTS
AReportoftheColoradoRiverGovernanceInitiative1
April,2013
Introduction
InpreviouspublicationsoftheColoradoRiverGovernanceInitiative(CRGI),weconcludedone
ofthemostimportantsourcesofuncertaintyinthebasinarethelegaluncertaintiesregarding
theobligationsoftheUpperBasintoreleasewatertotheLowerBasin.Specifically,wehave
highlightedthreerelatedandhighlysalientquestions:(1)doestheUpperBasinhavean
obligationtodeliver7.5MAF/yeardownstream(onaverage)forLowerBasinconsumption;(2)
doestheUpperBasinhaveanobligationtodeliverhalftheMexicanTreatyobligation(0.75
MAF/year)downstream;and(3)canthefailuretoachieveoneorbothoftheseobjectives
triggeracompactcall?2Thesearefundamentalquestions,astheylargelydeterminelongterm
wateravailabilityinthebasin.Buttheyarealsolargelyignoredquestions,asuptothispoint,
norulingonthesequestionshasbeenrequiredtooperatethesystemafortunatebyproduct
ofUpperBasindemandsstillbeinglowenoughtoallowbothofthepresumeddelivery
obligationstobefulfilled.Wherethesequestionscurrentlyariseareinlongtermsystem
modeling,thelatestexamplebeingworkconductedfortheColoradoRiverBasinWaterSupply
andDemandStudy(theBasinStudy).3
Unfortunately,duetopoliticalsensitivities,theBasinStudydidnotprovide,orattemptto
provide,adirectanalysisofthesequestions,asthemodelingassumptionswereconstructedin
awaytominimizetheneedforcontroversiallegalassumptions.Thisisbestillustratedbythe
conceptofmiraclewater.InmodelingscenariosinwhichtheUpperBasincouldphysically
notdeliver7.5MAFdownstreamwithoutcurtailingUpperBasindepletions,theapproachwas
toallowUpperBasinusestoproceedwithoutcurtailmentwhilemagicallyconjuringupthe7.5
MAFdesiredbytheLowerBasinandinjectingitintothesystemdownstreamofLeesFerry
evenifitwouldnotphysicallyexistinreality.Thissatisfiesthelegalinterpretationsand
politicalobjectives
of
both
basins:
the
Lower
Basin
receives
the
7.5
MAF
which
they
believe
is
1Formoreinformation,[email protected] orCRGIDirectorDougKenney([email protected]).2Themostcompletesummaryoftheseargumentshavebeenpublishedas:Robison,Jason,andDouglasS.
Kenney.2013.EquityandtheColoradoRiver.EnvironmentalLaw,42(4):11571209[availableat:http://law.lclark.edu/live/files/13155robisonkenneyfinalforwebsitepdf].Avarietyofsupportingdocuments
canbefoundattheColoradoRiverInformationPortalathttp://waterpolicy.info/projects/CRIP/index.html.3http://www.usbr.gov/lc/region/programs/crbstudy/finalreport/index.html
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owedto
orclarifi
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subtract
doneto
interpre
interpre
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UpperB
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blishedasFig
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ct,andthe
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mulations,
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pperBasin
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e7.5MAF/
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Basindepl
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resngblocked
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ear(avera
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rmflows.
ctionofLo
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vetomake
ldrequire
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ompactcal
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ckofthe
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e).
While
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fwater
lcurtailmen
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hicallysho
rageFlows4
eInterimRe
rmationPort
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is
is
gal
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n
ortof
l:
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ThesharpdeclineinUpperBasinwateravailability5istheunavoidableconsequenceofhaving
toreleasewaterdownstreambeforesatisfyingUpperBasindemandswhich,again,isapointof
legaldispute,inpartbasedontheCompactwordinginSectionIII(d)thatdoesnotdescribe
thesereleasesasandeliveryobligation,andinpartonthepremiseofequitythatruns
through
the
Compact.
As
shown
in
the
Figure
1,
a
decline
in
average
streamflows
of
20%well
withinthescopeofmanyclimatechangestudiescouldresultinasituationinwhichLower
BasinwateravailabilityfromthemainstemisroughlytwicethatoftheUpperBasin,despitethe
intentoftheCompact(asshowninArticleIII(a))toallocateequalsharesamongbasins.
ImposingafirmobligationupontheUpperBasintodeliverpartoftheMexicanobligationonly
intensifiestheeffect.Obviously,thissqueezecouldhavecatastrophicconsequencesforUpper
Basinusers,leadingustospeculatethatthesituationwouldeitherneveroccuri.e.,a
negotiatedsolutionorsuccessfulUpperBasinlitigationwouldstopthecurtailmentsorwould
occuronlyaftersuccessfulLowerBasinlitigation.Anyofthesesolutions,however,couldtake
avarietyofformsandanumberofyearsperhapsdecadestocomplete,andtheoutcome
wouldhavesignificantandimmediateimpactsonwateravailabilityinbothbasins.Thislegal
uncertaintyhangsoverthebasinandhasforatleast65years6.Arguably,thissourceof
uncertaintyoutweighstheclimateanddemanduncertaintiesexposedandfeaturedintheBasin
Studyanalysis.
Thereisnowaytoallocatewaterdifferentlybetweenthetwobasinsthatresultsinanet
basinwidegaininwateravailability;itisazerosumeffort.Buttherearewaystoallocatewater
thatbalancestheriskofclimaterelatedshortagesmoreequitablybetweenbasins,andwhich
hasthebenefitofreplacinguncertaintywithcertainty.Inwatermanagement,thevalueof
certaintycannot
be
underestimated,
and
as
argued
above,
the
greatest
threat
to
certainty
is
themannerinwhichthelegalambiguitiesandomissionswillultimatelybeaddressed.Remove
http://waterpolicy.info/projects/CRIP/index.html.Thefigureisbasedonahostofhighly(andintentionally)
debatableassumptionsandsimplifications;thus,itshouldbeviewedasastartingpointfordiscussion,ratherthan
aformalprojectionorlegalinterpretation.Specifically,inscenarioswherethelongtermaverageLeeFerryflowis
14.5MAF/yearorhigher,itassumesthattheUpperBasinwillberequiredtomaintainaminimumdelivery
scheduleof8.23MAF/yearinordertosatisfytheCompactandTreaty,andthattheLowerBasinwillberequiredto
pass1.5MAF/yearofthiswatertoMexico,withtheremainderavailableforusebytheLowerBasin.Inscenarios
wherethelongtermaverageLeeFerryflowis14.0MAF/yearorless,itassumestheUpperBasinwillberequired
tomaintainaminimumdeliveryscheduleof8.18MAF/yearinordertosatisfytheCompactandTreaty,andthat
theLowerBasinwillberequiredtopass1.4MAF/yearofthiswatertoMexico.(Notethatthisfigurewas
developedprior
to
Minute
319;
those
rules,
if
modeled
here,
would
have
anegligible
impact
on
the
trend
lines
shownhere.)Allvaluesaremaximumwateravailableforusebeforesubtractingevaporationorotherlosses.5Notethattheavailabilityofwaterandtheentitlementorallocationofwaterareseparate(butobviously
related)issues.TheCompactisclearthattheUpperBasinisallocated7.5MAF/yearofconsumptiveuses(Article
III(a)),butvirtuallynoclimatescenario(paleo,historic,orfutureprojections)suggeststhisisarealisticpossibilityif
anobligationtopasswaterdownstreamexists.6ThisconcernispartofthesubtextoftheUpperBasinCompactnegotiations(circa1948)[transcriptsavailableat
http://lawpac.colorado.edu/record=b119651],andisreflectedinthedecisiontoallocateUpperBasinsharesin
percentagesratherthanfixedvalues.
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theselegaluncertaintiesandthedoorisopentoavarietyofdealsandcopingmechanisms,and
theneedtoprepareforlegalshockstothesystemareavoided.This,inanutshell,wasthe
motivationfortheUpperBasinVoluntaryDemandCapoptionsubmittedbytheCRGItothe
BasinStudyforanalysis.Thefactthatthisoptionandtheothersocalledgovernance
options
7
were
not
analyzed
is
the
motivation
for
this
memo.
TheDemandCapConcept
ThecentralideaoftheUpperBasinVoluntaryDemandCap(hereaftertheDemandCap)is
thattheUpperBasinagreestolimittotalUpperBasindepletionsatanegotiatedlevel(well
belowthetheoretical7.5MAF/year)and,inreturn,isassuredthatneitherthefederal
governmentnorthestatesoftheLowerBasinwillrequestorsupportadministrationofan
interbasincompactcallinanyperiodwhenstorageinLakePowellisinsufficienttomaintain
thepredetermined
downstream
release
objective.8
Establishing
the
value
of
the
cap
and
the
releaseobjectivearepointstobenegotiated;buttheprincipleistoestablishthesenumbersin
advanceofacrisisandwithoutaneedtolitigatetheomissionsandambiguitiesthatexistinthe
CompactandrelatedelementsoftheLawoftheRiver.Inthatregard,theDemandCapisnot
intendedtoreplaceoramendtheCompact9,butrather,isanoperationalregimeplacedontop
ofthisfoundationfollowingtheprecedentofthe2007InterimGuidelinesforLowerBasin
ShortagesandCoordinatedOperationsforLakePowellandLakeMead(InterimGuidelines).
AlsoanalogoustotheInterimGuidelines,enactmentofthevoluntaryagreementwouldrequire
theunanimousagreementofthesevenbasinstates,andindoingso,wouldestablisha
temporaryarrangement.
In
this
case,
the
proposed
operating
regime
would
remain
in
effect
foratermof40years,subjecttorenewal(nolaterthan10yearspriortoexpiration)by
affirmativeactionbyaminimumof5of7states.Theagreementcouldbemodifiedor
741of160submittedoptionswerecharacterizedasinvolvinggovernance;see
http://www.usbr.gov/lc/region/programs/crbstudy/finalreport/techrptF.html.8TheDemandCapproposalcanbefoundintwoslightlymodifiedforms:theoriginalversionintheBasinStudy
materials(option117at
http://www.usbr.gov/lc/region/programs/crbstudy/finalreport/Technical%20Report%20F%20
%20Development%20of%20Options%20and%20Stategies/Appendix%202%20
%20Options%20Submitted%20to%20the%20Study/Appendix%20F2%20
%20Options%20Submitted%20to%20the%20Study.pdf),andaslightlyupdatedversionontheColoradoRiver
InformationPortal
(http://waterpolicy.info/archives/docs/Upper%20Basin%20Voluntary%20Demand%20Cap,%20amended%20Feb%
202012.pdf?p=1683).Neitherversionisreprintedhereinitsentirelyasthefollowingsectionprovidesthemost
comprehensivearticulationandanalysistodate.9Infact,theDemandCapproposalisseenasawaytohonorandreinforcetheheartoftheCompact,whichisthe
commitmenttoanequalsharingofwateramongthetwobasins.
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terminatedatanytimebyunanimousagreementofthestates.Onceterminated,theLawof
theRiver,asitcurrentlyexists,providesthedefaultlegalandoperationalregime.
TheDemandCapisnotacompletelynewidea,asasimilarideawasoncefloatedataBasin
StudymeetinginAlbuquerque.10
Then,asnow,theidearaisesseveralconcerns.Firstand
foremost,while
the
value
of
eliminating
legal
uncertainty
is
undeniably
attractive
and
valuable,
thereisabenefitassociatedwithuncertaintyinthatitallowsallpartiestoretainhopeforthe
legalinterpretationthatbestsuitstheirinterests.ToagreetoacapforcestheUpperBasinto
concedeapracticalapportionmentsignificantlylessthan7.5MAF11;similarly,agreeingtothe
proposalforcestheLowerBasintoconcedethattheirapportionmentisnotseniortoallUpper
Basinuses(exceptUpperBasinPresentPerfectedRights).Forbothparties,theideamakes
senseonlytotheextentthattheconcessionsinvolvedaremorethanoffsetbythevalueof
thereducedlegaluncertaintyandtheotherancillarybenefitsoftheproposal.Insummary,
potentialbenefitsoftheDemandCap(ascomparedtothestatusquo)include:x ThethreatofaninterbasinCompactcalliscompletelyeliminatedtherebyprotecting
existingUpperBasinwaterusersfromacall,andeliminatingtherelianceofLowerBasin
usersonsuccessfullylitigatingacallasistheneedforanyinterim
litigation/negotiationconcerningtheexistenceofanUpperBasindeliveryobligation
andseveralrelatedlegalissues(includingtheUpperBasinsshareoftheMexican
deliveryobligationandtheuseofLowerBasintributaries);
x TheDemandCaparrangementprovidesmechanisms(namely,theUpperBasincaponconsumption)thatencouragethemaintenanceofstorageinLakePowell(andallthe
associatedbenefits
thereof,
including
drought
protection,
and
protection
of
recreation
andhydropowerindustries);
x Withtheexceptionofsomenewadministrativeexpenses(associatedprimarilywithtrackingUpperBasinconsumption),theDemandCapoptionrequiresnonew
expenditures,andinfactislikelytosavesignificantpublicfundsbyeliminatingor
reducingtheneedformanyexpensiveriskcopingstrategies,andbyreducingthe
financialcosts(andpotentialimpacts)oflitigation;and,
x Thearrangementprovidesafoundationuponwhichmanyemergingandnewreformscouldbeestablished,whilemaintainingtheexistingLawoftheRiverasthedefault
10See:Kuhn,Eric.2011.RiskManagementStrategiesfortheUpperColoradoRiverBasin.DraftofJune7.
11Arguably,thishasalreadyoccurredinUpperBasinreports,includingtheseminalstudybyTiptonandKalbach
(1965)estimatinglongtermUpperBasinwateravailabilityasrangingfrom4.7to6.3MAF/year.(Tiptonand
Kalbach,Inc.1965.WaterSuppliesoftheColoradoRiver.ReportpreparedfortheUpperColoradoRiverCommission.Denver,July.)ThisisalsodoneintheHydrologicDeterminations.
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condition.Bylargelyremovingortemperingthegamechanginguncertainties
(associatedwiththeeffectofclimatechangeonaverageandextremeflows,andthe
interpretationofkeyLawoftheRiverissues),theDemandCapestablishesan
environmentencouragingfurtherinnovations(includingriveraugmentation).
TheModelingEffort
Thefollowingmodelingwasconductedinsummerandfall2012usingCRSS12
byKevinWheeler,
ownerofWaterBalanceConsulting(andaproductoftheUniversityofColoradoCenterfor
AdvancedDecisionSupportforWaterandEnvironmentalSystems(CADSWES)).Thisworkwas
donecommensuratewiththeBasinStudyand,assuch,utilizedassumptionsfromthat
investigationwhereverpossiblewithafewnotableexceptions.Modelingresultsareshown
below,precededbyadiscussionofsomeprominentmodelingassumptionsandadjustments
thatshaped
the
study
design.
MethodologyandAssumptions
Themodelingapproachwastocomparetheperformanceofthedemandcapscenarioagainsta
statusquo(hereaftertheBaseline)scenario,primarilyfromthestandpointofconsumptionlevelsinbothbasinsandreservoirstorage.Thesearethemacrolevelvariablesofinterestin
anyoperationalregimethatmodifiestherelationshipbetweentheUpperandLowerBasin.For
bothscenarios,
inputs
(supplies)
derive
from
use
of
the
downscaled
GCM
projected
hydrology.
Thatclimaticscenario,whichassumeswarming,hasthefurtherinfluenceofaugmenting
demandsspecifiedintheBasinStudysScenarioAdemandschedule.13
Thesesupplyand
demandelementshaveavarietyofembeddedassumptionsandshortcomings,notdetailed
here,butwereselectedtodovetailtheanalysiswiththeBasinStudytotheextentpossible.
Similarly,weutilizedtheBasinStudytimehorizon,whichextendsto2060.Someofthe
benefitsoftheDemandCapproposalareprobablymoreevidentatlaterdates,butwecould
notexplorethispointwithoutaccesstosupplyanddemandscenariosextendingpast2060.
Toperformthiscomparison,afewelementsofCRSShadtobemodified.Asforeshadowed
earlier,themiraclewateralgorithmhadtobemodifiedintwoways.First,inthoseinstancesin
whichmiraclewaterwasutilizedintheBaselinescenarios,thosequantitiesweresubtracted
fromUpperBasinusetogetanaccuratevalueofhowmuchwatertheUpperBasinactually
12CRSSistheColoradoRiverSimulationSystem,aRiverWarebasedmodelthatistheofficialmodelusedbythe
BureauofReclamationforsystemoperationsandscenarioplanning.13
Theimpactofassumedwarmingondemandsissignificant,averageroughly0.5MAF/yearby2060.
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consumed.FailuretodosowouldmakecomparisonsoftheBaselinetotheDemandCap
scenariomeaningless.Second,themiraclewateralgorithmisunlimitedi.e.,theprogramcan
addinmorewaterthanwouldphysicallybemadeavailablefromUpperBasincurtailments.As
amatterofphysicsandpolicy,welimitedmiraclewatertotheamountthatcouldactuallybe
achieved
through
Upper
Basin
curtailments,
subject
to
the
protection
of
Upper
Basin
Present
PerfectedRights(whichweassumetobe2.2MAF).
AlsoproblematicwasthefactthatCRSSoperatesbasedondemands,notdepletions.Despite
thenameDemandCap,ourproposalis,inreality,adepletioncap.Additionally,insatisfying
demands,CRSStracksofwateravailabilityanddemandsinvariousreaches/tributaries,and
doesnotsatisfydemandsinagivenriversegmentwherewaterisphysicallyunavailable.For
thepurposesofouranalysis,thislevelofdetailissomewhatcounterproductive,asweassume
thatonceafirmcapisinplace,physicalandinstitutionaladjustmentswouldbemadetoensure
fulluseofthecap.AdjustmentsweremadetohittheUpperBasindepletionmaximums
describedin
the
Demand
Cap
scenarios.
BoththeBaselineandDemandCapscenariosrequiredrefinements.Ofthetwo,specifyingthe
Baselinescenariowasthelargerchallenge,asitrequiressomeassumptionsabouthowthe
currentrulesmightactuallybeinterpretedinpractice.Twoissuesareparticularlysalient.First,
themagnitudeoftheUpperBasindeliveryobligationhadtobespecifiedatsomelevel,with7.5
MAF/yearand8.25MAF/yearbeingobviouscandidates.Ratherthanchooseoneoftheother,
weutilizedbothvalues(thuscreatingtwoBaselinescenarios).Second,theInterimGuidelines
arescheduledtoexpirein2026ifnotrenewedormodified.Wechoosetokeepthese
guidelines
throughout
the
full
scenario.
To
the
extent
that
other
legal
assumptions
were
required,unlessotherwisenoted,weretainedtherulesalreadycodifiedinCRSS.
ThreeadjustmentstotheoriginalDemandCapscenarioarenotable.First,weoriginally
proposedusingacapvaluethatincludedUpperBasinevaporationlosses.Ultimately,we
decidedtospecifyanUpperBasincapnumberbeforeevaporation,whichimmunizedtheUpper
Basinfromthepracticalchallengeoftryingtopredictevaporationpreciselyinanygivenyear.
(Weassumethoselossestobeintheneighborhoodof0.5MAF/year.)Second,inorderto
investigatethepotentialbenefitsoftheDemandCapproposalinprotectingreservoirstorage,
wequicklyrealizedthatitmightbeadvisabletopreventtheLowerBasinfromusingsurpluses
attributableto
enforcement
of
the
Upper
Basin
cap.
To
do
this,
aLower
Basin
cap
of
7.5
MAF/yearwasimposedthroughoutmostoftheDemandCapscenarios.Andthird,through
initialmodelingrunswedeterminedthatanUpperBasincapof4.5MAF/year(notcounting
evaporation)wasthebestvalueforillustratingthetradeoffsinherenttotheDemandCap.
(Theoriginalproposalsuggested5.5MAFroughly5MAFindepletionsand0.5MAFin
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evaporationasastartingpointofanalysis.)Ofcourse,weencouragesubsequentanalyses
thatfeatureabroaderrangeofvalues.
Results
Theresultspresentedbelowarefromthesixth(andfinal)iteration,bywhichtimethekey
modelingissuesdescribedabovehadbeenidentifiedandresolved.Eachfigureprovidesresults
forthreescenarios:
75Prot22 Thisbaselinescenarioassumesadeliveryobligationaveraging7.5MAF/year.
FailuretodeliverthisvolumeresultsinUpperBasincurtailmentsasnecessary
tomeetthisdelivery,withthecaveatthat2.2MAFofUpperBasinPresent
PerfectedRightsarealwaysprotectedfromcurtailment(hencetheProt22
nomenclature).
82.5Prot22 Thisbaselinescenarioassumesadeliveryobligationaveraging8.25MAF/year.
Aswith75Prot22,failuretodeliverthisvolumeresultsinUpperBasin
curtailmentsasnecessarytomeetthisdelivery,withthecaveatthat2.2MAF
ofUpperBasinPresentPerfectedRightsarealwaysprotectedfrom
curtailment.
4.5DoubleCap ThisDemandCapscenarioallowstheUpperBasintodeplete4.5MAF/year
beforeevaporativelosses(roughly0.5MAF/year),andadditionallycaps
LowerBasin
consumption
at
7.5
MAF/year.
No
Upper
Basin
delivery
obligationisenforced(i.e.,noCompactcalls).
Afewfiguresplottwoadditionalvariables:
ASchedule(withClimateChange) ThesearetheprojectedUpperBasindemandsfromthe
BasinStudyScheduleAdemandscheduleasadjusted(increased)toreflect
theaddeddemandsassociatedwiththedownscaledGCMprojected
hydrology.
4.5SingleCap ThisDemandCapscenarioallowstheUpperBasintodeplete4.5MAF/year
beforeevaporativelosses(roughly0.5MAF/year).NocaponLowerBasin
consumptionisenforced.NoUpperBasindeliveryobligationisenforced(i.e.,
noCompactcalls).
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Collectively,thesevariablesallowustotrackdifferencesinhowtheDemandCapaffectswater
availability(measuredintermsoftheamountofconsumptionallowed)andchangesin
reservoirstorage.Asapracticalmatter,watermanagersarelikelytowanthighlevelsofboth
variables,althoughinrealitythereisafixedquantityofwater,andmaximizingboth
consumption
and
storage
at
all
times
is
an
impossibility.
Similarly,
it
is
an
impossibility
to
simultaneouslyincreasewaterconsumptionandstorageforallusers;inputstothesystemare
notmodifiedacrossallthescenariosi.e.,theyallusethesamedownscaledGCMprojected
hydrologysothisisazerosumexercise.Thus,thewaytoevaluatetheresultsistocompare
thequantitativetradeoffsintermsofsupplies(asmeasuredbyconsumption),storage(as
measuredbyreservoirvolume/elevation),andreliability,andtodothiswithrespecttothe
nonquantitativetradeoffsassociatedwiththeeaseofmaintainingthestatusquo(offeredbytheBaselinescenarios)versusthebenefitsofeliminatinglegaluncertainties(offeredbythe
DemandCapscenarios).
Giventhe
importance
of
these
non
quantitative
variables,
it
is
impossible
for
us
to
impartially
establishanyscenarioasthewinnerorbest,andthus,toarguefororagainstenactmentof
theDemandCappolicy.Butthatisnotthepointofthisexercise.Thepointistoillustrate
tradeoffsandopportunitiesassociatedwiththepursuitofagovernancebasedsolution,inthis
case,aDemandCapscenario.WhetherornottheDemandCapisagoodapproachiscertainly
debatable;whetherornotgovernancebasedreformsshouldbepartofthesearchforsolutions
isnot.Basinleaderswillsoonbeforcedtomakedecisionsregardingseveralgovernanceand
LawoftheRiveritems,includingextensionoftheInterimGuidelines;thedefinitionofUpper
Basindeliveryobligations,ifany,totheLowerBasinand/ortoMexico;thedesignand
implementation,ifany,
of
an
interbasin
Compact
call;
the
quantification
of
Upper
Basin
Present
PerfectedRights;andsoon.Again,muchoftheappealoftheDemandCapisthatitcan
subordinateorcompletelyeliminatemanyofthemostdivisiveissues,anddosoinawaythat
leavestheCompactunalteredandasthedefaultinstitutionalframework.
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Depletions:Upper asin
10
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Depletions:Lower asin
11
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ReservoirStorage
12
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FindingsandConclusions
Theprecedingfiguresillustratesomeofthemostimportanttradeoffsassociatedwithadopting
theDemandCapproposal.Asnotedearlier,thedatadoesnotallowustomakeadefinitive
rulingaboutwhichapproachisbest,butitdoesallowustospeculateonthetradeoffs
(assuminga4.5
MAF
cap)
that
would
be
central
to
any
decision
making.
What
we
believe
to
be
thesalientlessonsofFigures2through7aresummarizedbelow.
Depletions:UpperBasin
Theplotofaveragedepletions(Figure2)isperhapsmostnotableforshowinghowboththe
BaselineandDemandCapscenariosfallwellbelowthedemandsassociatedwithScheduleA
anddownscaledGCMprojectedhydrology.TheDemandCapdoesnotsolvethisproblemof
unmetdemands,
but
neither
does
either
Baseline.
14
Thus,
this
plot
is
abetter
illustration
of
the
UpperBasinsupply/demandmismatchthanitisinstructiveinilluminatingasolution.
ThePDF(probabilitydistributionfunction)showninFigure3illustratesakeyfeatureofthe
DemandCap,asUpperBasindepletionsarerelativelyflatandstablewhencomparedtothe
Baselinescenarios.Overall,theBaselinescenariosofferslightlymorewaterabout60%ofthe
timeandslightlylessabout40%ofthetime,withbigdifferencesseenonlyattheextremes.Of
course,muchofwatermanagementisfocusedonmanagementattheextremes.
Overall,theUpperBasindepletionfiguresillustratethat,whiletheDemandCapconceptmight
firstseem
like
aradical
and
significant
concession
for
the
Upper
Basin,
the
effect
during
the
studyperiodisrelativelymodestatleastatthe4.5caplevel.Extendingthetimehorizonpast
2060wouldlikelyyieldmoredramaticresults,aswouldchangingtheclimatehydrology
assumptions.Ultimately,fortheUpperBasin,thekeydecisionsarewhetherornotlosingthe
extremehighsisworthbeinginsulatedagainsttheextremelows,andwhetherornottabling
thelegalissues(forthetermoftheagreement)ispreferabletoleavingthoseopen.
Depletions:LowerBasin
Notsurprisingly,theplotofaverageLowerBasindepletions(Figure4)showstheneteffectof
theDemandCapistolimitLowerBasindepletionsbelowwhatwouldbepossiblegiventhe
Baselinescenariosassumingenforcementofeithera7.5MAF/yearor8.25MAF/yearUpper
14ItisquitepossiblethatCRSSoverestimatestheUBshortagesforeachofthesescenarios,inthattheresolutionof
themodeldoesnotincludesomeexistingstoragereservoirsand,thus,mayunderestimatetheabilityofthe
systemtomeetsomedemands.
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Basindeliveryobligationalthoughthedifferencesarenotextreme(notetheyaxisdivisions
areonly200KAF).Again,whetherornottheLowerBasincanrealisticallyexpecttosurmount
thelegalandpoliticalhurdlesassociatedwithenforcingeitherdeliveryobligationisastrategic
considerationthatcannotbeshownquantitatively.IntheDemandCapscenario,theLower
Basin
is
not
required
to
pursue
(or
prevail
in)
such
litigation.
TheotherkeystrategicconsiderationfortheLowerBasinistheeffectoftheDemandCapon
watersupplyreliability.ThePDF(Figure5)showsvirtuallynosignificantdifferencesin
reliabilityovermostoftheruns,withthenotableexceptionofthelowesttailwhichshowshow
theDemandCapshiftssomeoftheclimaterisktotheLowerBasin.Thisisaninherentand
predictableconsequenceofeasingsomeoftheclimateriskontheUpperBasin(explained
earlierandshowninFigure1).TheDemandCapisassumedtoamelioratethisconcernby
betterprotectingreservoirstorage,thesubjectofthefollowingsetoffigures.
ReservoirStorage
TheimpactoftheDemandCaponreservoirstorageisconsistentlypositivei.e.,betterthan
eitherBaselinescenario,andespeciallynotableinthelateryearsoftheruns.AverageLake
Meadelevation,forexample,isroughly20feethigherintheDemandCapscenariothanthe7.5
MAF/year(75Prot22)scenarioby2060(Figure6).ThestoryforLakePowellisalso
consistentlypositive,inthattheDemandCapresultsingreaterstoragethaneitherBaseline
(Figure7).
NotethatFigure7alsoshowstheimpactofasinglecapi.e.,justanUpperBasincapas
originallyproposedonreservoirstorage.Thedoublecapwasutilizedinthismodelingfor
fearthat,withouttheLowerBasincap,anygainsinLakePowellreservoirstoragemightbelost
tosurplususesdownstream.Figure8showsthesefearswereprobablyoverblown,asno
discernibleimpactisseenforLakePowell.
Conclusions
Overall,the
modeling
of
the
Demand
Cap
shows
that,
compared
to
the
statusquo,this
institutionalreformcan(a)betterbalancetheriskofwatersupplyperturbationsassociated
withclimatechangebetweentheUpperandLowerBasins,(b)eliminatemanysignificantlegal
uncertainties,and(c)protectandenhancereservoirstorage,allwhilehavingmodestimpacts
onwateravailableforconsumptiveuseinbothbasins.Whetherornotthisisviewedasan
improvementoverthestatusquoisamatterofpersonaljudgment,andrestsonassumptions
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aboutwhatthestatusquomightactuallyentail.Itisworthnotingthat,formodelingpurposes,specifyingtheBaseline(statusquo)scenariosprovedmuchmoredifficultthantheDemandCap,whichisapowerfulreminderthatsignificantlegalomissionsandambiguitiesexistinthe
LawoftheRiverduringperiodsofwaterscarcity.
Thatagovernance
reform
can
mitigate
against
both
hydrologic
(climate
change)
and
legal
uncertaintiesisevidencethatthisclassofreformsneedtobeconsideredprominentlyinthe
searchforsolutions,despitetheiromissionintheBasinStudyanalysisandthehesitancyof
manypartiestodiscussmattersoflawandpolitics.Thefactis,thethornylegalandpolicy
issuesthatexistwillatsomepointdemandresolution,andthetimetodothatisbeforethe
reservoirsareemptyandthespecterofaCompactcallhastakencenterstage.Conceptually,
solutionsthatprotecttheCompactfromlegalchallengesshouldhavebroadappeal;the
DemandCapisonepathwaytothatfuture.